The problem of identity theft comes up frequently on the WeLL, this is a nice programmatic start.
footle » Protecting Your Users’ Data with a Privacy Wall The idea is simple: don’t have any direct links in your database between your users’ “public” data and their private data. Instead of linking tables directly via a foreign key, use a cryptographic hash [1] that is based on at least one piece of data that only the user knows—such as their password. The user’s private data can be looked up when the user logs in, but otherwise it is completely anonymous.